My b 4000 4.0 litre misses while driving and backfires on deceleration.have done tune up,fuel pump,regulator,and filter.took the catalyst off and at idle its missing.have also replaced the intake plenum gaskets.it seemed to help my idling problem.but i still need to know whats causing the missing and backfiring.please help!!!!!!!!!
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reason is usually from unburnt fuel being ignited in exhaust --some causes need tune up--running rich--to short an exhaust system-exhaust leak /////yes you have a fuel regulator for your fuel injection the rebuild kits are inexpensive and are easy to do
Or maybe too much fuel-backfiring in the exhaust is the burning of the unburnt fuel in the exhaust. Check the fuel pressure. You can rent fuel pressure gauges at autozone, I believe. If too low, possibly a bad filter or bad pump. If too high, test the fuel pressure regulator. a failed regulator can let extra gas into the engine through the vacuum line on it. Take off the vacuum line to the regulator, and watch the regulator for a minute with the engine running. If gas starts oozing out of the vacuum port at the pressure regulator, the regulator has failed and must be replaced.
If pressure is correct, at least you have eliminated that as a problem. Check the air filter, check spark plugs and plug gaps, more or less back to basic tune up.
Have the misfire diagnosed and the backfiring will be fixed also. The backfiring is caused by the "over-rich" fuel mixture in the exhaust stream and is igniting within the exhaust. Fix the misfire (which will cause the rich condition) and the backfire will be gone.
misfiring can also be from low fuel pressure and faulty injectors and not electrical alone. Run fault codes instead of guessing and costing money and have a fuel pressure test done on the fuel manifold to check for faulty pump-fuel pressure regulator and filters
Check your fuel pressure it should be 60-66 psi with the key on and engine off.If its not within these specs then the fuel pump is faulty and needs to be replaced.If the fuel pressure is within the specs then remove the mass air flow sensor and clean the small wires inside of it using a non-chlronated brake cleaner then let it dry for 10 minutes and re-install it.
It may take as much as 60 PSI to overcome the fuel pressure regulator. No, you can't blow through it. I suspect you have a fuel starvation issue. It could be a clogged fuel filter. It may more likely be a pressure leak inside the tank. That pressure gauge you mentioned comes highly recommended at this point. There is a flexible line connecting the pump to the metal line in the tank. If it ruptures, you have only minimal pressure, and the vehicle starves for fuel. Using the gauge, turn the ignition on and off a couple of times, (do not start) If the filter is choked, you will still achieve pressure to overcome the regulator. If it never makes that much pressure, then it is the flex or the pump itself. My first experience with this I found the rupture after the third pump! Embarrassing!
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If I understand your concern, you have backfiring when decelerating, if yes, a possibility is that your air/fuel ratio is too lean, there is too much air and/or too little fuel. This could also be brought about by using free breathing air filter (such as K & N) instead of the original air box/filter and no re-jetting/re-calibration done. Either that or the exhaust system has been modified or replaced with free flow, headers or sport tuned. If yes, then either the carbs have not been re-jet or the injector has not been re-calibrated. It may also require re-mapping of the ECU.
Depressing the clutch when decelerating disengages the load and therefore no engine breaking is happening.
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.
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